In an induction motor, AC (alternating current) electrical power energizes windings of a stator, creating a rotating magnetic field that is characterized as having a stator flux. The stator flux induces electric current in windings of the rotor. The rotor experiences a torque, and rotates under load at a rate that is slower than the rotation speed of the stator flux. The difference between the rotation rate of the rotor and the rotation rate of the stator flux is the slip speed, and the difference between positions of the rotor and the stator flux is called the slip angle. The changing flux that the rotor sees as a result of difference in rotation speed from the stator flux is called the rotor flux.
Two popular types of induction motor controllers, and the algorithms which these use, are direct torque control (DTC) and field oriented control (FOC). In DTC, torque and stator flux are controlled using coordinates in a stator alpha and beta reference frame, i.e. coordinates relative to the a and b phases of the stator, with calculations in a stationary coordinate system. In FOC, rotor flux, torque current quadrature component and rotor flux direct component are controlled using coordinates in a rotor d and q reference frame, i.e. coordinates relative to the direct and quadrature axes of the rotor, with calculations in a rotating coordinate system that rotates synchronously with the rotor. Each type of induction motor controller has advantages and disadvantages. Therefore, there is a need in the art for a solution which overcomes the drawbacks of the systems described above.